Linux Shell

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Introduction

This contains details of each command of the shell. Multiple commands can be passed as a single argument with colon(;) separation.

Commands

1. pwd

   • Displays the name of the current working directory.

2. echo

   • Displays the the string passed as argument.

3. cd

   • It changes the current working directory to the directory passed as an argument.

   • Implemented in cdCommand.c

4. ls

   • Displays the list of all files and directories in the specified directory.

   • Flags -l and -a accounted for.

   • Also handles multiple directories as arguments.eg. ls -al dir1 dir2

   • Implemented in lsCommand.c

5. fg and bg processes (System Commands)

   • Is able to run any process in background or foreground.

   • Upon exit(or kill) of a background process ,it displays the name and PID of the killed process.

   • Implemented is sysCommands.c

6. pinfo

   • Displays various information about the process whose PID is passed as an argument.

   • Implemented in pinfo.c

7. history

   • Displays the last 'n'(n<=20) commands exectued by the shell.

   • Also works upon exit and restart of the shell.

   • Implmented in history.c

8. kjob

   • Takes a job ID of a bg process and sends a signal number to that process.

   • Implemented in kjob.c

9. fg & bg

   • fg : Brings a bg process to foreground.

   • bg : Changes state of stopped bg process to running.

10. setenv and unsetenv

    • setenv : Creates or changes the value of an env variable.

    • unsetenv : Destroys the env varialbe.

11. overkill

    • Terminates all the bg process.

12. Input/Output Redirection with Piping

13. Signal Handling

    • Ctrl-D : quits the shell

    • Ctrl-Z : Pushes a fg process to background.

    • Ctrl-C : Interrupts a fg process.

Note :

• The maximum length of a command is restricted to 1024 characters.

• Maximum no. of commands passed at a time is restricted to 100.

• When a backgorund process is killed and the message is displayed. Press Enter to restore the prompt.